Fibrous sheets are used for a variety of different purposes and are comprised of an array of different fibers, binders and fillers. For example, fibrous sheets can be used as acoustical ceiling tiles, paper products and furniture board. Primarily, fibrous sheets can be comprised of mineral wool, perlite, cellulosic fibers, fillers and binders.
Fibrous sheet production utilizes combinations of fibers, fillers, bulking agents, binders, water, surfactants and other additives mixed into a slurry and processed into a fibrous sheet. Examples of fibers used may include mineral fiber, fiberglass, and cellulosic material. Mineral wool is a lightweight, vitreous, silica-based material spun into a fibrous structure similar to fiberglass. Cellulosic material is typically in the form of newsprint. Added fillers may include expanded perlite, brighteners such as titanium oxide and clay. Expanded perlite reduces material density and clay enhances fire resistance. Examples of binders used in fibrous sheets include starch, latex and reconstituted paper products, which link together and create a binding system locking all ingredients into a structural matrix.
Organic binders, such as starch, are often the primary component providing structural adhesion for the fibrous sheet. Starch is often the preferred organic binder because it is relatively inexpensive. For example, fibrous sheets containing newsprint, mineral wool and perlite are often bound together by starch. Starch imparts both strength and durability to the fibrous sheet structure.
Unfortunately, there is a limit on how much starch can be added before such properties begin to decline. Starch is highly water-soluble and when partially hydrated loses a portion of its ability to bind the fibrous sheet components. Additionally, water-felted and cast panels tend to exhibit limited stability under high moisture loads given the hydrophilic nature of the cellulosic fibers. Furthermore, fibrous sheet strength and durability cannot simply be enhanced by using increased quantities of starch and cellulose, since starch increases a fibrous sheet's susceptibility to moisture and sag.
Thus, a high degree of starch and cellulose can lead to sagging and weakening of the board under humid conditions. Also, fibrous sheets having large quantities of starch require elevated drying rates or increased drying time to remove excess water from the board. Therefore, there a need for a method for increasing both the strength and durability of a fibrous sheet without the addition of increased quantities of starch. Additionally, there is a need for a fibrous sheet that is not susceptible to sagging under high moisture loads and does not require increased drying times during processing.